Valid, reliable, and efficient self-report assessments of symptoms of chronic diseases are necessary for clinical research. Although there have been many advances in the psychometrics of patient-reported outcomes (PROs), there has been an absence of information about their association with patients' daily experiences of symptoms in their daily lives. Ensuring the ecological validity of PROs is paramount, because most PROs rely on retrospection over relatively long reporting periods (weeks to months) and cognitive science research has shown that recall of subjective states is prone to bias. The advent of electronic diaries and associated methods for collecting patient data has made it possible to assess PROs in the field. The goal of this project is to determine the ecological validity of existing PRO items and scales (content selected in collaboration with Network Centers associated with this RFA). We hypothesize that revising items according to the reporting period specified, the instructions provided to patients, the item response options, and item content can improve ecological validity. Several studies examining pain and fatigue in chronically-ill rheumatologic and neurological patients will test this hypothesis by comparing momentary diary data with recall data. Broader contextual influences on patient performance with PRO items will also be examined. For the Network Projects, we propose providing the diary methodology and expertise to assess ecological validity for the collaborating Centers, including the assessment of global impression of change measures in the context of clinical trial.